1. Field of the Invention
The present invention relates to the decryption of encrypted transmissions, and more particularly to a system, a device and a method for providing hybrid conditional access for receivers of encrypted transmissions.
2. Description of the Related Art
Providers of cable television (CATV) service transmit a signal to subscribers via a cable. The signal contains multiple channels distributed within the frequency range of the signal. The CATV service providers typically encrypt their transmission signals for preventing non-subscribers from utilizing the signals. In order for the subscriber's TV or VCR to utilize the signal, a means must be provided for receiving the signal, decrypting the signal, and selecting a channel. The means provided is typically a device, known as a set-top box. The set-top box is connected to a cable for receiving the signal transmitted by the CATV service provider. The set-top box is further connected to the subscriber's TV or VCR for providing a signal, which is ready for display. The set-top box typically provides a navigation function and a security function. The navigation function is for navigating and selecting channels within the received signal. The security function is for decrypting the received signal. The security function of the set-top box is part of a conditional access (CA) system for determining the entitlements of the subscriber's set-top box to the services provided by CATV service provider.
According to laws mandated by the FCC, the navigation function must be kept separate from the security function. This has typically been accomplished by set-top boxes having either a separate permanent security function embedded within the set-top boxes, or a separate removable security function in the form of a smart card that interfaces with the set-top box.
There are disadvantages to providing a set-top box with only an embedded security function. The security function in the set-top box is fixed. When critical features within the control access system are changed, the security function in the set-top box becomes non-functional. For example, cable service providers may periodically change the encryption method used, and may offer or require different levels of entitlement to certain channels to their subscribers. In order to accommodate a change in entitlement or encryption method, a new set-top box with a different security function is required to replace the original one. Furthermore, each set-top box has to be custom made as specified by the CATV service provider, thus incurring high manufacturing costs.
Providing the set-top box with a removable security function provides the ability to change the security function of the set-top box without having to replace it. Furthermore, a standard set-top box could be used for a variety of CATV service providers, thus lowering manufacturing costs. However, there are disadvantages to providing a set-top box with only a removable module providing the security function. Upon absence or disengagement of a removable module the set-top box overrides the navigating function and is unable to decrypt any of the received transmissions. Without the removable module the set-top box is only able to show content that is not encrypted—content that is not of high value.
EP Application Number 0 585 833 A1, entitled Video Signal Decoder System discloses a set-top box for decoding video signals in which the box includes two security function modules: an embedded security function module and an interchangeable smart card security function module which interfaces with the box. However, the disclosed box has a number of disadvantages. Upon receiving a signal, decryption is performed by one of the security function modules. The security function module is selected by the box via a trial and error method. The embedded security function module is tested first for selection, and the smart card is tested second. The security function module of either the embedded security function or the smart card security function that is selected depends on which has a decryption algorithm that corresponds to the encryption algorithm of the received signal. Thus, the selection of one security function module to perform decryption is made according to the signal received by the box, with the other security function module being disabled. The box thus does not provide a default security function module. The box does not allow different levels of access to the received transmission.
U.S. Pat. No. 5,742,680 discloses a set-top box for providing decryption of a received signal, wherein the signal is sent by a selected transmitter from a plurality of transmitters, and the decryption is performed by a corresponding smart card of a plurality of smart card security function modules. The box does not include an embedded security function module. Without a corresponding smart card for the signal selected, the set-top box cannot perform decryption.
In the aforementioned references, any holder of a smart card can use the smart card with any compatible set-top box. However, providers of transmitted signals often find it to their advantage to restrict decryption of their signals to the set-top box belonging to the subscriber. Furthermore, the aforementioned references do not provide for checking of entitlement to decrypt the transmitted signals. Nor do they disable security functions modules that are no longer entitled. In order to prevent non-entitled decryption, providers of signal transmissions must change the encryption algorithm of the transmitted signals. This would require distribution of new smart cards to all entitled customers.
EP Application 0 570 785 A1 discloses a method for allowing decryption of transmitted signals at defined geographic locations, using smart cards. However, to accomplish this the above method requires transmission of at least two data channels to be received by at least two separate processors.